968 ME. W. p. PYCEAKT ON THE [DeC. 13, 



been so imperfectly ossified as to release the supra-occipital entirely 

 from the epiotic. 



The exoccipital forms the iufero-lateral border of the foramen 

 magnum; from the point where it joins the supra-occipital it runs 

 upwards and outwards under the epiotic: its supero-lateral external 

 border is bounded in part by a large tract of cartilage forming the 

 outer wall of the floccular fossa, and in part, below this tract, by 

 the prootic. The ventrilatei'al border is ensheatlied in cartilage 

 and produced downwards to form the paroccipital process. Seen 

 from within, it is found to be fused with the opisthotic, the boundary- 

 line between the two bones being indicated only by a faint notch 

 lying just in front of the condyloid foramen. 



The lambdoidal suture does not quite correspond with the ridge 

 of that name. This arises from the middle of the posterior border 

 of the squamosal, and running upwards for a short distance along 

 the posterior border of the parieral parts company with the margin, 

 where it curves downwards over the epiotic and continues its curve 

 transversely ; ultimately to meet in the middle line a little short 

 of halfway between the coronal and lambdoidal sutures. 



The parietals have the form of oblong plates of bone running 

 transversely across the skull (PI. LXI. fig. 3). The frontal border 

 is rounded off dorsally at the point where the two parietals meet 

 in the middle line ; the same region of the frontals is similarly 

 deficient, hence a small diamond-shaped frouto-parietal fontauelle 

 is formed. The alisphenoid border is very narrow in ApUnochjtes, 

 being encroached upon by the squamosal ; in Splieniscus and 

 CaturrJiactes it is broad, rather more than | the total width 

 and incurved. In Pij(joscelis it is of medium breadth — about | the 

 total width, and only slightly curved. The squamosal border in 

 Apienodytes is more than four times the extent of that of the 

 alisphenoid border ; iu Sjjlieniscus and Catarrhactes the squamosal 

 and ahsphenoid borders are of about equal length ; in Fi/r/oscelis 

 the squamosal border is about twice that of the alisphenoid and 

 perfectly straight. The supra-occipital border develops a strong 

 out-standing ridge which runs downwards to the squamosal. This 

 ridge leaves the free border of the parietal almost imnjediately 

 after it passes over from the squamosal, and runs upwards, in the 

 case of SjiJieniscus, to the level of the dorsal limit of the supra- 

 occipital, but does not meet in the middle line. The development 

 of this crest, at this stage, closely resembles the permanent 

 condition of that of Aptenochjtes and PijgosccUs, and, in a slightly 

 lesser degree, that of Catarrhactes and Eudyptula, since in the 

 adults of these latter the crest is more developed laterally. In the 

 adult Splieniscus this parietal crest forms the large out-standing 

 plate of bone — the squamoso-parietal wing — which runs upvtards 

 to join the narrow median sagittal crest. In this way the posterior 

 portion of the deep " temporal fossa " is formed. 



The frontals undergo marked change of form before reaching 

 the adult condition. They form paired plates of considerable size 

 extending forwards, under the nasals, as a pair of divaricating 



